Insulin is produced by the islets of Langerhans within the pancreas, and the specific hormone-producing cells which make insulin are called the beta cells. Insulin helps most cells of the body take up biological fuels, including the sugar glucose. As pancreatic beta cells are killed during the onset of juvenile diabetes, the pancreas stops producing this hormone, and glucose accumulates in the blood, giving rise to abnormally high glucose levels that are a sign of diabetes. The body then becomes dehydrated as the kidneys overwork to filter the excess glucose into the urine. Meanwhile other body cells essentially starve in a sea of plenty and begin to uncontrollably break down their stores of fat and protein to provide more fuel. If such breakdown of fat continues unchecked, acidic by-products, i.e. ketones, build up which, combined with dehydration, can induce coma and death.
Insulin injections are generally able to halt this lethal sequence and prevent it from recurring, but they cannot mimic the normal pattern of insulin release by the pancreas. Moreover, they cannot normalize metabolic functioning well enough to prevent the long term complications of diabetes which are generally believed to be caused or exacerbated by chronically elevated blood glucose levels.
The beta cells of the pancreas are destroyed in various ways, and one is believed to be via an autoimmune process. Although animal insulin and the more modern recombinant human form thereof offer temporary treatment in response to the destruction of the beta cells and thus survival for millions of diabetics, neither offers a cure because injections or other administration of insulin must be taken once or more a day for life. In addition, many diabetics eventually suffer from devastating complications, including heart disease, blindness and kidney failure.
Advances in automated methods to isolate human pancreatic islets have increased the availability of preparations rich in endocrine tissue for clinical and laboratory research directed to insulin production and related aspects of diabetes. These efforts have led to the first successful, albeit transitory, transplantation of islets into a Type 1 diabetic patient and to the establishment of an islet distribution center which supplies human islets for research to investigators in the United States.
Pancreatic islets do not grow readily in primary cultures; however, these endocrine cells have been grown with difficulty as monolayers. The difficulty of long-term culture has not only hindered the laboratory research for such islets, but it has also hindered attempts to carry out physiological and even clinical studies with such islets. It had been previously shown that it is possible to eliminate inherently contaminating fibroblasts in monolayer cultures of neonatal pancreatic islets by keeping the islets free-floating in petri dishes for 5 days before the transfer of the islets to coated dishes. Because this approach was not always feasible and because the survival of adult islets was curtailed under these conditions, fibroblast contamination has remained a problem.
The addition of various inhibitors of fibroblast proliferation has not yet solved this problem. More specifically, to rid islet cultures of fibroblasts to the culture medium, attempts were previously made to add the following compounds as inhibitors of fibroblast growth: thimerosal (Kaiser, N. et al., Endocrinology, 123, 834-840, 1988), iodoacetic acid (Shimuzu, S. et al., Endocrinol. Jpn., 31, 253-261, 1984) and 2-deoxyglucose (Yoshida, K., et al., B.B.R.C., 108, 279-285, 1982). However, these efforts were met with only limited success, and generally investigators were faced with the decantation of pancreatic cell suspensions into new dishes after each few hours of culture, followed by culture in a medium which is free of cysteine and serum, Hayek, A. et al., In Vitro, 25, 146-150 (1989). Therefore, improved ways of maintaining pancreatic islets in culture continue to be avidly sought.